Prab at 03:29, 4 June 2023

2023-06-04T03:29:53Z

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'''Prothrombin time''' (PT) is a blood test that measures the time it takes for a clot to form in a blood sample after certain clotting factors have been added. It is primarily used to evaluate the extrinsic and common pathways of the [[coagulation]] cascade, and is particularly important in monitoring the effectiveness of [[anticoagulant]] therapy, such as with warfarin.<ref>{{cite journal|last=Tripodi|first=A|title=The laboratory and the direct oral anticoagulants|journal=Blood|year=2013|pmid=23335186|doi=10.1182/blood-2012-11-459865}}</ref>
[[File:Coagulometer.jpg|thumb|Coagulometer]]
== Procedure and Interpretation == 

The prothrombin time test is performed on a sample of a patient's blood. This sample is mixed with a substance called tissue factor (also known as thromboplastin), which initiates the clotting process. The time taken for the blood to clot is then measured and reported as the prothrombin time. The result is often expressed relative to the control sample, in a value known as the international normalized ratio (INR).<ref>{{cite book|last=Dacie|first=JV|title=Practical Haematology|year=2012|publisher=Elsevier|isbn=978-0702051479}}</ref>

The normal range for PT varies from laboratory to laboratory but is generally around 11 to 14 seconds. A prolonged PT indicates a deficiency in the factors of the extrinsic or common coagulation pathways, or the presence of an inhibitor. If a patient is on anticoagulant therapy, a longer PT is expected and indicates the effectiveness of the treatment.<ref>{{cite journal|last=Keeling|first=D|title=Guidelines on oral anticoagulation with warfarin - fourth edition|journal=British Journal of Haematology|year=2011|pmid=21671894|doi=10.1111/j.1365-2141.2011.08753.x}}</ref>

== Clinical Use == 

Prothrombin time is used in various clinical situations:

* Monitoring patients on [[warfarin]] therapy
* Evaluating the cause of unexplained bleeding or bruising
* Checking for low levels of clotting factors
* Assessing liver damage, as the liver produces clotting factors<ref>{{cite journal|last=Northup|first=PG|title=Coagulation in liver disease: a guide for the clinician|journal=Clinical Gastroenterology and Hepatology|year=2013|pmid=23419359|doi=10.1016/j.cgh.2013.02.014}}</ref>
== Limitations and Challenges == 

While PT is a valuable tool in assessing clotting function, it has some limitations. The test only measures the function of certain clotting factors, so it may be normal even when a person has a bleeding disorder. Other tests, like activated partial thromboplastin time (aPTT), may be used in conjunction with PT for a more comprehensive evaluation of a patient's coagulation system.<ref>{{cite journal|last=Cuker|first=A|title=Coagulopathy testing in patients with acute ischemic stroke|journal=Stroke|year=2011|pmid=21940965|doi=10.1161/STROKEAHA.111.626853}}</ref>
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{{Myeloid blood tests}}
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[[Category:Blood tests]]
[[Category:Coagulation system]]
[[Category:Medical monitoring]]

Prothrombin time - Revision history

Prab at 03:29, 4 June 2023